Preheat oven to 350F. Grease and flour three 6" cake rounds, line with parchment.
In a medium bowl, whisk cake flour, baking powder, and salt. Set aside .
In a small measuring cup, combine mashed bananas and buttermilk.
Beat butter until smooth. Add sugar and beat on med-high until pale and fluffy (2-3mins).
Reduce speed and add eggs one at a time, fully incorporating after each addition. Add vanilla and mix until well combined.
Alternate adding flour mixture and buttermilk mixture, beginning and ending with flour (3 additions of flour and 2 of buttermilk). Fully incorporating after each addition. Do not overmix.
Gently fold in chocolate chips.
Spread batter evenly into prepared pans and bake for 35-40mins or until a toothpick inserted into the center comes out mostly clean.
Place cakes on wire rack to cool for 10mins then turn out onto wire rack to cool completely.
Peanut Butter Swiss Meringue Buttercream:
Place egg whites and sugar into the bowl of a stand mixer, whisk until combined.*
Place bowl over a double boiler on the stove and whisk constantly until the mixture is hot and no longer grainy to the touch (approx. 3mins). Or registers 160F on a candy thermometer.
Place bowl on your stand mixer and whisk on med-high until the meringue is stiff and cooled (the bowl is no longer warm to the touch (approx. 5-10mins)).
Switch to paddle attachment. Slowly add cubed butter and mix until smooth.**
Add vanilla and peanut butter and and whip until smooth.
Place one layer of cake on a cake stand or serving plate. Top with 2/3 cup of frosting. Sprinkle with 2 Tbsp chopped peanuts. Repeat with remaining layers and apply a thin coat of frosting all over the cake. Chill for 20mins.
Frost the cake. Smooth the sides and top of the cake then use a 1M tip to pipe dollops on top with remaining frosting.
Do a border of peanuts and chocolate chips along the bottom if desired.
*Ensure there is NO trace of egg yolks in your whites and that your mixer bowl and whisk is completely grease free or your meringue won't stiffen. ** The buttercream may look like it's curdled at some point. Keep mixing until it is completely smooth.